The present invention relates to a method of diagnosing the degradation of a glow plug and the presence or absence of the abnormality of the glow plug, and more particularly, to a method that improves reliability in diagnosis and the like.
Since the quality of a glow plug, which is used in an internal combustion engine such as a diesel engine, significantly affects the startability or the like of a diesel engine or the like, various methods, apparatuses, and the like for diagnosing the quality, the degree of degradation, and the like of the glow plug, have been proposed and been put to practical use in the past.
For example, a method and the like that measure a resistance value of a glow plug at the time of energization, compare the resistance value with a single threshold, and determine the quality of the glow plug on the basis of the result of the comparison are known well (for example, see JP-A-2010-127487 and the like).
However, a diagnosis result having sufficient reliability may not be obtained from the comparison with a single threshold due to product variation of each glow plug, difference in the degradation state caused from using each glow plug, or the like.